This invention relates to transmissions and especially to synchronising devices for a transmission and a transmission provided with a synchronising device. The invention is particularly advantageous in the field of transmission in heavy vehicles, such as trucks and buses.
Most modern vehicles are fitted with a synchronized gear box. In such a gear box, the teeth of the gearwheels are permanently meshed. The action of the gear selector is thus not to engage or disengage the teeth of the actual gear, but instead to lock its rotation to the shaft that runs through its hub. When a gear is disengaged, it is unlocked from the shaft and rotates freely.
Locking the shaft with a gearwheel is achieved by means of a so called dog collar. It is splined to, and thus rotates with, the shaft and has gear-like teeth which may engage with corresponding teeth on the gearwheel. The engagement of the two set of teeth lock the rotation of the gearwheel to the dog collar, and thus also to the shaft.
However, if the dog collar and the gearwheel are spinning at different speeds, the teeth will fail to engage and a loud grinding sound will be heard as they clatter together. For this reason, modern dog collars have a synchroniser mechanism that prevents the teeth from making contact before the rotating speeds of the two parts are synchronized. These synchronisers usually comprise a cone clutch and a blocking ring. The cone clutch brings the gearwheel and the dog collar to the same rotational speed using friction, and the blocking ring prevents the teeth from making contact by means of oblique blocking surfaces interacting with corresponding blocking surfaces on the gearwheel. As the speeds are synchronized, the friction force on the blocking ring is revealed and it twists slightly, allowing, engagement of the teeth.
However, the dog collar has to be brought towards gearwheel quite slowly in order to give the blocking surfaces of the dog collar a fair chance to find the corresponding blocking surfaces. If the blocking surfaces fail to find each other, they will not interact and thus cannot prevent the teeth of the dog collar from making contact with the teeth of the gearwheel before their rotational speeds are synchronized.
There is thus a need for an improved synchronising device at least partly removing the above mentioned disadvantage.
It is desirable to provide a product for synchronization of two rotating parts where the previously mentioned problem is at least partly avoided.
The disclosure concerns a synchronising device for synchronising a first rotatable part with a second rotatable part adjacent to said first rotatable part. The synchronising device comprises a first part provided with an engaging sleeve and a second part provided with a synchroniser ring. The first part may typically be a shaft, and the second part may typically be a gearwheel arranged upon an adjacent shaft.
The engaging sleeve is provided with a first set of internal teeth enabling a rotationally fix and axially displaceable arrangement upon said first part, and a first conical friction surface. The engaging sleeve is adapted to be positioned in a first and in a second axial position. In the first axial position, the first set of internal teeth engages only with said first part. Thus, in the first axial position, the first and second parts are not interconnected and the two shafts may rotate independently of each other. In the second axial position, the first set of internal teeth engages with both said first and said second part. Hence the two parts are rigidly interconnected and the two shafts are bound to rotate at the same speed.
The synchroniser ring is provided with a mating conical friction surface adapted to interact with the first conical friction surface in order to synchronise the engaging sleeve and the synchroniser ring, i.e. the first and second parts. Preferably and most commonly, the first conical friction surface is constituted by an internal cone and the mating conical friction surface is constituted by an external cone. The synchroniser ring is further provided with a second set of internal teeth that enables arrangement upon said second part. The second set of internal teeth is provided with a first blocking surface adapted interact with a corresponding second blocking surface upon the second part. The interaction of the blocking surfaces blocks a rotational movement of the synchroniser ring relative to the second part during synchronisation of the rotational speeds of the first and second parts.
The synchroniser ring is adapted to be positioned in a first and a second rotational position relative to the second part. The first rotational position enables said blocking surfaces to interact with each other and the second rotational position enables an axial displacement of the synchroniser ring. The synchroniser ring is further adapted to be positioned in a first and a second axial position. In the first axial position of the synchroniser ring, said blocking surfaces can interact with each other, and in the second axial position the blocking surfaces of the synchronising ring are positioned such that they not face the blocking surfaces of the second part, enabling an axial displacement of the engaging sleeve.
The synchroniser device is characterised in that it has at least one axial positioning resilient member which is arranged to act upon the synchroniser ring and the second part. The axial positioning resilient member is arranged such relative said synchroniser ring and said second part that it exercises a force upon said synchroniser ring in direction towards its first axial position, i.e. towards the first part, when the synchroniser ring is in any position between its first and second axial positions. The force exercised by the at least one axial positioning resilient member is enough to press the synchroniser ring towards its first axial position as long as the engaging sleeve is in, or on its way to, its first axial position. However, the force exercised by the at least one axial positioning resilient member on the synchroniser ring is substantially smaller than the force exercised on the synchroniser ring by the engaging sleeve moving towards its second axial position, i.e. towards the second part. Hence, the axial positioning of the synchroniser ring carried out by the at least one axial positioning resilient member is easily overcome by moving the engaging sleeve in direction of the second part.
The axial positioning resilient member keeps the synchroniser ring in its first position, unless the engaging sleeve acts upon the synchroniser ring in the opposite direction, i.e. towards the second part. With the axial positioning, the synchroniser ring is arranged in the correct axial position for its blocking surfaces to interact with the blocking surfaces on the second part. The synchronising device can be provided with blocking surfaces such that it is able to synchronise rotations in both rotational directions. The axial positioning, also results in less drag losses between the friction surfaces of the engaging sleeve and the synchroniser ring since by preventing the friction surface of the synchronising ring from unintentionally rattling against the conical friction surface of the engagement sleeve. The disclosed arrangement also enables a synchroniser device with fewer parts than in traditional synchronising devices due to the fact that the synchroniser ring acts directly upon the second part, thus providing a simpler and less expensive solution. Further, larger conical friction surfaces can be provided on the engaging sleeve and the synchroniser ring, because the friction surfaces can be provided with a large radius and still be inside the engaging sleeve outer radius, due to that fewer parts are arranged between the engaging sleeve and the second part.
Further advantages are achieved by implementing one or several of the features of the dependent claims.
The at least one axial positioning resilient member may be provided in the synchroniser ring and acts upon an axial reaction surface of said second part, wherein said axial positioning resilient member and said axial reaction surface are arranged such relative each other, that said axial positioning resilient member exercises a force upon said synchroniser ring in direction towards its first axial position. However, it would also be possible to arrange the at least one axial positioning resilient member in the second part, and the corresponding axial reaction surface on the synchroniser ring.
The axial reaction surface may have a radial inwardly directed inclination in an axial direction of said first part. When the axial positioning resilient member acts upon the inclined surface, a reactive force will be executed on the synchroniser ring, in direction towards its first axial position. As a result, synchroniser ring moves axially towards its first axial position, the resilient member sliding upon the inclined surface.
The radial inwardly directed inclination may have a transition to a radial outwardly directed inclination directed in an axial direction of said first part at an end of said axial reaction surface arranged close to said first part. The transition between the inwardly and outwardly directed inclinations forms a groove that functions as a stop for the axial positioning resilient member. The groove prevents the axial positioning resilient member from forcing the synchroniser ring further towards the first part, since its sliding motion is stopped by the groove. The synchroniser ring is in its first axial position when the axial positioning resilient member is positioned in said transition between the inwardly and outwardly inclined axial reaction surfaces. Alternatively, another form of groove or stop can be arranged upon the rotational reaction surface, such as a protrusion or groove or shoulder, instead of the transition between the inwardly and outwardly directed inclinations.
The axial reaction surface may be provided upon a first external tooth of the second part. Such an arrangement provides an advantageous manufacturing process, since the axial reaction surface may be created by an after-treatment process, such as grinding or milling off a portion of a tooth of the second part.
The synchroniser ring may be provided with a plurality of axial positioning resilient embers substantially equally spread about said synchroniser ring. Preferably, the synchroniser is provided with at least three essentially evenly spread out axial positioning resilient members. With axial positioning resilient members acting on the synchroniser ring in evenly spread out points, a balanced positioning of the synchroniser ring can be achieved, avoiding unwanted tilt of the synchroniser ring. Here, evenly spread means that small deviations from absolute evenness are allowed as long as they are small enough in order to be easily compensated for by the internal friction of the device, i.e. between the different parts of the device.
In a preferred embodiment the synchroniser ring is further provided with at least a rotational positioning resilient member, which acts upon a rotational reaction surface of said second part, wherein said rotational positioning: resilient member and said rotational reaction surface are arranged such relative each other, that said rotational positioning resilient member exercises a force upon said synchroniser ring in direction towards its first rotational position. The purpose of the rotational positioning resilient member is thus to bring the synchroniser ring towards its first rotational position. Having the synchroniser ring already provided in its first rotational and axial positions when the synchronisation is to start, i.e. at contact between the conical friction surfaces, results in faster and more reliable synchronisation since the blocking surfaces are already in contact and consequently in the correct position to interact with each other. With both axial and rotational positioning of the synchroniser ring, the synchronisation can be performed faster, because no time has to be spent on letting the corresponding blocking surfaces find each other—they are already in contact when the synchronisation starts. It would also be possible to arrange the rotational positioning resilient member in the second part, and the corresponding rotational reaction surface on the synchroniser ring. However, due to the rotational positioning, the synchroniser device can only synch the rotations between the first and the second parts for that direction the blocking surfaces are adapted for. The inventive synchronising device is therefore especially suitable to be arranged as a range and/or splitter synchronisation.
The axial and rotational positioning members may preferably be constituted by spring loaded plungers.
The rotational reaction surface may be provided with an inclination directed radially inwardly in a circumference direction of said second part. When the rotational positioning resilient member acts this inclination, a reactive force will push the synchroniser ring in the direction towards it first rotational position.
The inclination directed radially inwardly in a first circumference direction of said second part may have a transition to a radial outwardly directed inclination in said first circumference direction of said second part. The transition between the inwardly and outwardly directed inclinations forms a groove that functions as a rotational stop for the synchroniser ring—here is the first rotational position. The groove prevents the rotational positioning resilient member from forcing the synchroniser ring further in rotational direction. Thus, when the rotational positioning resilient member is positioned in the transition between the inwardly and outwardly inclined rotational reaction surfaces, then the synchroniser ring is positioned in its first rotational position. Alternatively, another form of groove or stop can be arranged upon the rotational reaction surface, such as a protrusion or groove or shoulder, instead of the transition between the inwardly and outwardly directed inclinations.
The rotational reaction surface may be provided upon a second external tooth of the second part. Such an arrangement provides an advantageous manufacturing process, since the rotational reaction surface may be created by an after-treatment process, such as grinding or milling off a portion of a tooth of the second part.
As an alternative to or in combination with inclined rotational reaction surfaces, the rotational positioning resilient member may be arranged with direction of action having an angle to a radial direction of the synchronising ring. The rotational positioning resilient member can thereby become a larger lever for the spring force.
An alternative position of the rotational reaction surface is constituted by a flank of an external tooth of the second part. Such an arrangement utilizes the original geometry of the external tooth of the second part, and thus no after-treatment such as grinding or milling is needed.
The synchroniser ring may be provided with a plurality of rotational positioning resilient members substantially equally spread about said synchroniser ring. Preferably, the synchroniser is provided with at least three evenly spread out rotational positioning resilient members. With axial positioning resilient members acting on the synchroniser ring in evenly spread out points, a balanced positioning of the synchroniser ring can be achieved, avoiding unwanted tilt of the synchroniser ring. Here, evenly spread means that small deviations from absolute evenness are allowed as long as they are small enough in order to be easily compensated for by the internal friction of the device, i.e. the friction between the different parts of the device.
The engaging sleeve may be provided with a groove provided in an axial central position among said first set of inner teeth. The groove is adapted to interact with a detent resilient member arranged in the first part. The detent resilient member acts radially outwards such that it holds the engaging sleeve in its first position, in which it only engages with the first part.
Said detent resilient member may be able to hold said engaging sleeve in its second position, by protruding outside the first set of inner teeth. The detent resilient member thus keeps the engaging sleeve in an engaged position, preventing it from unintentionally unlocking the rotational motions of the first and second parts.
Said detent resilient member is preferably a spring loaded plunger.
The axial resilient positioning member and the rotational axial positioning member can be provided as individual resilient members or as a combination member, performing both the axial and the rotational positioning. If the rotational and axial positioning members are integrated in the same resilient positioning member, the reaction surfaces are correspondently adapted.
The invention further concerns a transmission provided with a synchronising device as described above.